Variable width memory module supporting enhanced error detection and correction

ABSTRACT

Described are memory modules that support different error detection and correction (EDC) schemes in both single- and multiple-module memory systems. The memory modules are width configurable, and support the different EDC schemes for relatively wide and narrow module data widths. Data buffers on the modules support the half-width and full-width modes, and also support time-division-multiplexing to access additional memory components on each module in support of enhanced EDC.

FIELD OF THE INVENTION

The subject matter presented herein relates generally to computermemory.

BACKGROUND

Personal computers, workstations, and servers include at least oneprocessor, such as a central processing unit (CPU), and some form ofmemory system that includes dynamic, random-access memory (DRAM). Theprocessor executes instructions and manipulates data stored in the DRAM.

DRAM stores binary bits by alternatively charging or dischargingcapacitors to represent the logical values one and zero. The capacitorsare exceedingly small, and their stored charges can be upset byelectrical interference or high-energy particles. The resultant changesto the stored instructions and data produce undesirable computationalerrors.

Some computer systems, such as high-end servers, employ various forms oferror detection and correction to manage DRAM errors, or even morepermanent memory failures. The general idea is to add storage for extrainformation that can be used to identify or correct for errors. By wayof example, conventional servers that support error correction commonlyinclude pairs of memory modules, each of which provides burst of 72-bitdata for each memory access, for a total of 144 bits. Sixteen of thesebits are used for error correction, so that each memory accesseffectively provides 128 bits of information. This level of redundancyallows support for error detection and correction (EDC) robust enough tocorrect for any single DRAM device failure, and any multi-bit errorsfrom any portion of a single DRAM device. An exemplary EDC technology ofthis type is marketed under the trademark Chipkill™.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a memory system 100 in which a motherboard 105 supports amemory-controller component 110 that communicates with a memory module115 via nine pairs of nibble-wide primary data ports DQu/DQv and aprimary command-and-address (CA) port DCA.

FIG. 2 depicts memory slice 125[0] of FIG. 1 in accordance with oneembodiment.

FIG. 3A depicts memory slice 125[0] with DRAM components 130A and asubset of the signal lines highlighted to illustrate how multiplexers200, 205, and 210 convey data between primary data traces DQp and pairsof DRAM components 130.

FIG. 3B is a waveform diagram 300 illustrating successive readtransactions directed to memory slice 125[0] configured as illustrated3A.

FIG. 4A depicts memory slice 125[0] with DRAM components 130A and thesignal lines highlighted to illustrate how multiplexers 200, 205, and210 convey data between primary data traces DQp and pairs of DRAMcomponents in a time-division-multiplexing (TDM) mode that can be usedfor enhanced EDC.

FIG. 4B is a waveform diagram 400 illustrating successive readtransitions directed to memory slice 125[0] with memory module 115 inthe TDM mode, illustrated in FIG. 4A.

FIG. 4C is a waveform diagram 410 illustrating successive readtransactions directed to memory slice 125[0] with memory module 115 in asecond TDM mode.

FIG. 5A depicts a memory system 500 in which a computer motherboard (orsystem backplane) 505 includes module connectors 510 and primary datalinks DQp[71:0] and DQt[35:0] for connecting one or a pair of modules115 to memory controller component 110 using point-to-point dataconnections.

FIG. 5B depicts a memory system 550 in which the same motherboard 505 ofFIG. 5A is populated with two memory modules 115A and 115B.

FIG. 6A depicts memory slice 125[0] with one DRAM component 130B and asubset of the signal lines highlighted to illustrate how multiplexers200, 205, and 210 convey data between primary data link group DQp[3:0]and one DRAM component in a half-width mode.

FIG. 6B is a waveform diagram 600 illustrating successive readtransactions directed to memory slice 125[0] configured as illustratedin FIG. 6A.

FIG. 7A depicts memory slice 125[0] with DRAM components 130A and thesignal lines highlighted to illustrate how multiplexers 200, 205, and210 convey data between primary link group DQp[3:0] and a pair of DRAMcomponents in a half-width TDM mode that supports enhanced EDC.

FIG. 7B is a waveform diagram 700 illustrating successive readtransitions directed to memory slice 125[0] with memory module 115 inthe enhanced EDC mode illustrated in FIG. 7A.

FIG. 7C is a waveform diagram 710 illustrating successive readtransitions directed to memory slice 125[0] with memory module 115 inthe half-width enhanced EDC mode illustrated in FIG. 7A.

FIG. 8 details a portion of memory module 115, introduced in FIG. 1,highlighting features and connectivity that support widthconfigurability and different EDC modes in accordance with oneembodiment.

FIG. 9A depicts a memory system 900 similar to system 500 of FIG. 5A,with like-identified elements being the same or similar.

FIG. 9B depicts a memory system 950 in which the same motherboard 505 ofFIG. 9A is populated with two memory modules 905A and 905B, eachconfigured in a narrow, half-width mode.

FIG. 9C is a waveform diagram 960 illustrating successive readtransitions directed to memory slice 925[0] of memory module 905A ofFIG. 9B in an enhanced EDC mode similar to that detailed previously inconnection with FIG. 7A.

FIG. 10A depicts a memory system 1000 in which a pair of memory slices125[0], one from each of two memory modules 115A and 115B, areconfigured to support a two-module enhanced EDC mode in which all theDRAM components 130 accessed in a single memory transaction are on thesame module.

FIG. 10B depicts memory system 1000 of FIG. 10A with DRAM components 130of slice 125[0] of module 115B activated in support of a memorytransaction.

FIG. 10C is a more complete view of memory system 1000 of FIGS. 10A and10B.

FIG. 10D is a waveform diagram 1050 illustrating a read transitiondirected to memory slice 125[0] of memory module 115A, as illustrated inconnection with FIGS. 10A and 10C.

DETAILED DESCRIPTION

FIG. 1 depicts a memory system 100 in which a motherboard 105 supports amemory-controller component 110 that communicates with a memory module115 via nine pairs of nibble-wide primary data ports DQu/DQv and aprimary command-and-address (CA) port DCA. The eighteen data ports DQuand DQv are connected to module 115 via four-trace subsets ofseventy-two primary data links DQp[71:0]; CA port DCA conveys modulecommands via primary CA link group DCA[26:0].

Memory module 115 includes nine memory slices 125[8:0], each of whichincludes four DRAM components 130 and a data-buffer component 135. DRAMcomponents 130 are divided into an anterior pair 130A and a posteriorpair 130B, where “anterior” and “posterior” refer to the two sides ofmemory module 115. Seventy-two secondary data links DQs[71:0] connectDRAM components 130A to data-buffer components 135, and anotherseventy-two secondary data links DQs[143:72] likewise connect DRAMcomponents 130B to data-buffer components 135. Each data-buffercomponent 135 selectively conveys data between one or more of fournibble-wide secondary link groups DQs and a pair of the nibble-wideprimary data link groups DQbp. Considering memory slice 125[0], forexample, data buffer 135 communicates data between secondary link groupsDQs[3:0], DQs[7:4], DQs[75:72], and DQs[79:76] and primary link groupsDQbp[3:0] and DQbp[7:4].

An address-buffer component 140, alternatively called a “RegisteredClock Driver” (RCD), relays module commands received from controllercomponent 110 via primary address interface DCA[26:0] to each memorycomponent 130 via one of three secondary command interfaces QCAB, QCCD,and QCEF. Address-buffer component 140 also controls the flow of datathrough data-buffer components 135 via a common buffer interface BCOM.

Memory module 115 supports multiple operational modes that offerdifferent levels of error detection and correction. In a first accessmode, each data-buffer component 135 communicates pairs of four-bit (x4)data nibbles, in four-pair bursts, between respective link groups DQuand DQv of controller component 110 and a corresponding pair of DRAMcomponents 130. Responsive to a read command from controller component110, for example, slice 125[0] delivers a four-bit burst of nibble-wide(four-bit) data from each of DRAM components 130A or 130B to controllercomponent 110 via two primary link groups DQp[3:0] and DQp[7:4]. Withnine such slices 120[8:0], each read command thus provides controllercomponent 110 with eighteen data nibbles (72-bits) in four-bit bursts.Of each set of 72-bits, eight are for error-correcting code (ECC). Theredundancy provided by the additional eight bits provides for automaticcorrection for single-bit data errors, and guaranteed detection oftwo-bit data errors.

Memory module 115 also supports a second access mode that supportsenhanced error correction. In this second mode, each data-buffercomponent 135 employs time-division multiplexing (TDM) to communicatepairs of data nibbles, in eight-pair bursts, between respective linkgroups DQu and DQv of controller component 110 and both pairs of DRAMcomponents 130A and 130B. Considering only the lowest-order primary linkgroup DQp[3:0], for example, data-buffer component 135 of slice 125[0]interleaves bursts of four nibbles on secondary interfaces DQs[3:0] andDQs[75:72] to deliver a burst of eight nibbles on primary link groupDQp[3:0]; and similarly interleaves bursts of four nibbles on secondaryinterfaces DQs[79:76] and DQs[7:4] to deliver a burst of eight nibbleson primary link group DQp[7:4]. There being nine slices 125[8:0], eachread command thus provides controller component 110 with eight bursts ofeighteen data nibbles (72-bits). Controller component 110 groups theresultant eight sets of 72-bit data into four sets of 144-bit data, ofwhich sixteen bits of each set are used for error correction. This levelof redundancy allows support for error detection and correction (EDC)robust enough to correct for any single DRAM device failure, and anymulti-bit errors from any portion of a single DRAM device. An exemplaryEDC technology of this type is marketed under the trademark Chipkill™.

Address buffer 140 directs the different modal behavior of slices125[8:0] by providing control instructions to data-buffer components 135via a buffer command bus BCOM. Module 115 can be statically configuredat initialization to enter one of the modes by e.g. setting aconfiguration field in a mode register 145. Mode register 145 can beloaded by a slow signal interface (based on information stored in aserial Presence Device (SPD) via an SPD bus, an 12C bus, or somethingsimilar), or by a high speed bus (e.g., via the DCA group). Moderegister 145 can be located elsewhere, or mode configuration can beaccomplished using e.g. a configuration pin or jumper.

Each data-buffer component 135 includes two four-bit primary data portscoupled to a respective pair of link groups DQu and DQv via a primarydata interface 150. Each of slices 125[8:0] communicates word-wide(eight-bit) data, so memory module 115 communicates with controllercomponent 110 via seventy-two traces DQbp[71:0]. On the other side ofdata-buffer components 135, the eighteen anterior DRAM components 130Aprovide the low-order secondary data bits DQs[71:0] and posterior DRAMcomponents 130B the high-order secondary data bits DQs[143:72]. In slice125[0], for example, data-buffer component 135 includes four nibble-widesecondary data ports DQs[3:0], DQs[7:4], DQs[75:72], and DQs[79:76].

FIG. 2 depicts memory slice 125[0] of FIG. 1 in accordance with oneembodiment. Each of DRAM components 130A and 130B includes amemory-component interface DQ[3:0] connected to data-buffer component135 via a respective one of the four secondary data link groupsDQs[3:0], DQs[7:4], DQs[75:72], and DQs[79:76].

Data-buffer component 135 includes multiplexing logic that isrepresented here using three multiplexers 200, 205, and 210. Thefollowing examples illustrate data flow in the read direction, frommemory components 130A and 130B to primary traces DQbp[7:0] responsiveto read commands from controller component 110. Multiplexers 200 and 205support the two modes detailed previously. That is, multiplexers 200 and205 can present data from either pair of DRAM components 130A or 130B asa burst of four eight-bit words on port DQbp[7:0], or can present datafrom both pairs of DRAM components 130A and 130B as burst of eighteight-bit words on port DQbp[7:0]. Write data is conveyed similarly inthe respective modes, but from controller component 110 to the DRAMcomponents 130A and 130B. Data steering and timing are controlled byaddress-buffer component 140 via communication bus BCOM.

The third multiplexer 210 supports narrow data modes to be detailedlater. Briefly, a first narrow mode allows four-bit data from any one ofthe four DRAM components 130A and 130B to be presented on the low-orderprimary link group DQbp[3:0]; a second narrow mode allows four-bit datafrom two of DRAM components 130A and 130B to be time-divisionmultiplexed and presented sequentially or interleaved on the low-orderprimary link group DQbp[3:0] responsive to a single memory command; anda third narrow mode is like the second but the primary link groupDQbp[3:0] operates at twice the bit rate of the secondary link groups tothe DRAM components. An optional multiplexer 213 allows narrow data tobe presented on either of the low- and high-order primary buffer linkgroups DQbp[3:0] and DQbp[7:4] from any of secondary link groupsDQs[3:0], DQs[7:4], DQs[75:72], and DQs[79:76] to provide greaterrouting flexibility.

FIG. 2 additionally shows alternative arrangements 215 and 220 for pairsof DRAM components 130A and 130B in cross section. Arrangement 215includes two stacks of eight DRAM dies interconnected by e.g.through-silicon vias. Stacks of components 130A and 130B are on eitherside of module substrate 225, and each includes a master die 230 withthe requisite data-buffer logic. In the other illustrated alternativearrangement 220, DRAM components 130A and 130B are two-package stacks,one on either side of module substrate 225. Other alternativearrangements, with the same or different numbers of dies or packages,can also be used.

FIG. 3A depicts memory slice 125[0] with DRAM components 130A and asubset of the signal lines highlighted to illustrate how multiplexers200, 205, and 210 convey data between primary data traces DQbp and pairsof DRAM components 130. Secondary command interface QCAB includeschip-select (CS) lines (FIG. 8), which select DRAM devices (FIG. 8) inone of the two pairs of DRAM components, one device in each ofcomponents 130A in this example. Responsive to signals on buffer controlinterface BCOM, multiplexers 200, 205, and 210 communicate read andwrite data between primary link group DQbp[3:0] and the leftmostselected DRAM component 130A and between primary link group DQbp[7:4]and the rightmost selected DRAM component 130A. Should DRAM components130B be selected, then multiplexers 200 and 205 would select theiralternative connections. Each of slices 125[8:0] thus communicates aburst of four eight-bit words for each read or write transactioninitiated by controller component 110. In this context, a “transaction”is an atomic interaction a memory controller initiates by issuing amemory command (e.g., read or write) to cause one or more memory modulesto store or provide data.

FIG. 3B is a waveform diagram 300 illustrating successive readtransactions directed to memory slice 125[0] configured as illustrated3A. Signals associated with the first read transaction are encompassedin bold boundaries to distinguish them from those of the second readtransaction.

To begin, controller component 110 issues an activate command ACT tomodule 115 via CA traces DCA[26:0] to activate a row of memory cells(not shown) in a pair of DRAM components, anterior components 130A inthis example. Address buffer 140 buffers these signals and, after adelay time t_(buf), issues them to each slice 125[8:0] via the threesecondary command interfaces QCAB, QCCD, and QCEF. These secondaryinterfaces are identical, with each serving three sets of memory slices125. This example focuses on slice 125[0] for simplicity, so FIG. 3Bonly shows the signals presented on secondary command interface QCAB.

Having activated a row of memory cells, controller component 110 issuesa read command RD. Address buffer 140 buffers these signals and issuesthem to each of slices 125[8:0] via the three secondary commandinterfaces QCAB, QCCD, and QCEF to select columns of the memory cellswithin the active rows. The activate and read commands ACT and RD onsecondary command interface QCAB are separated by the row-cycle tocolumn-cycle delay time t_(RCD), and the selected memory components 130Apresent their data on secondary interface DQs[7:0] after a column-accessdelay t_(CAC). Data-buffer component 135 conveys the read data from theactive rows and columns of DRAM components 130A via lines DQs[7:0] ofthe secondary data interface and conveys it to controller component 110via traces DQp[7:0] of the primary data interface. In this example, thecommand interfaces operate at 1.6 Gb/s, half the 3.2 Gb/s speed ofprimary data traces DQp[71:0] and secondary traces DQs[143:0].

In this example, controller component 110 issues second activate andread commands ACT and RD directed to the posterior DRAM components 130B.The signal flow is similar to that discussed above in connection with anaccess to DRAM components 130A, except that data-buffer component 135directs data from the high-order secondary data interface DQs[79:72] totraces DQp[7:0] of the primary data interface.

FIG. 4A depicts memory slice 125[0] with DRAM components 130A and thesignal lines highlighted to illustrate how multiplexers 200, 205, and210 convey data between primary data traces DQbp and pairs of DRAMcomponents in a time-division multiplexing (TDM) mode that can be usedfor enhanced EDC. Slice 125[0] operates in the manner noted above inconnection with FIG. 3A, but address-buffer component 140 activates arow in all four DRAM components 130A and 130B to present four-bit dataon all four secondary data ports of data-buffer component 135.Data-buffer component 135 interleaves the data from the selected pairsof DRAM components 130 so that slice 125[0] communicates a burst ofeight eight-bit words—and module 115 communicates nine bursts of eighteight-bit words—for each read or write transaction initiated bycontroller component 110.

FIG. 4B is a waveform diagram 400 illustrating successive readtransitions directed to memory slice 125[0] with memory module 115 inthe TDM mode, illustrated in FIG. 4A, that corrects for any single DRAMdevice failure, and any multi-bit errors from any portion of a singleDRAM device (e.g., Chipkill™ EDC). Signals associated with the firstread transaction are encompassed in bold boundaries to distinguish themfrom those of the second read transaction.

To begin, controller component 110 issues an activate command ACT tomodule 115 via CA traces DCA[26:0] to activate a row of memory cells(not shown) in all four DRAM components 130A and 130B. Address buffer140 buffers these signals and, after a delay time t_(buf), issues themto each memory slice 125[8:0] via the three secondary command interfacesQCAB, QCCD, and QCEF. As with the example of FIG. 3B, this case focuseson slice 125[0] and so shows only shows the ACT signals presented onsecondary command interface QCAB.

Having activated a row of memory cells, controller component 110 issuesa read command RD. Address buffer 140 buffers these signals and issuesthem to each slice 125[8:0] via the three secondary command interfacesQCAB, QCCD, and QCEF to activate columns of the memory cells within theactive rows. Data-buffer component 135 reads a burst of four eight-bitwords from each pair of DRAM components 130A and 130B, on respectivesecondary lines DQs[7:0] and DQs[79:72], and interleaves the resultantdata to provide a burst of eight eight-bit words on primary data linksDQq[7:0]. As in the example of FIG. 4, the command interfaces operate at1.6 Gb/s, half the 3.2 Gb/s speed of primary data links DQp[71:0] andsecondary data links DQs[143:0]. “Bubbles” 405 between data bursts onsecondary data links DQs[79:72,7:0] accommodate the fact that slice125[0] has twice as many secondary data links as primary data links.

FIG. 4C is a waveform diagram 410 illustrating successive readtransactions directed to memory slice 125[0] with memory module 115 in asecond TDM mode. Signals associated with the first read transaction areencompassed in bold boundaries to distinguish them from those of thesecond read transaction. This example is similar to that of FIG. 4B, butbuffer 135 communicates over primary links DQp[71:0] at twice the bitrate relative to the bit rate employed with secondary links DQs[143:0].This embodiment relaxes the speed requirements for DRAM components 130Aand 130B, potentially reducing cost, power consumption, or both.

FIG. 5A depicts a memory system 500 in which a computer motherboard (orsystem backplane) 505 includes module connectors 510 and primary datalinks DQp[71:0] and DQt[35:0] for connecting one or a pair of modules115 to memory controller component 110 using point-to-point dataconnections. System 500 is shown to include a single memory channel,depicted using traces DQp[71:0], but can include additional channelssupported by the same or additional memory controllers.

Only half of primary traces DQp[71:0] extend directly—withoutintermediate components—to each of connectors 510. With reference tocontroller component 110, the link groups associated with signals DQuand DQv extend to the near and far connectors 510, respectively. In thissingle-module configuration, a continuity module 520 with electricaltraces 525 interconnects the primary interface link groups associatedwith signals DQu to link groups DQt[31:0], which extend via the farconnector 510 to half the contacts of primary data interface 150 of theone installed DRAM module 115. Motherboard 505 and continuity module 520thus provide point-to-point data connections between controllercomponent 110 and primary data interface 150. Module 115 is as detailedpreviously, and can support the modes detailed in connection with FIGS.3A, 3B, and 4A-4C.

FIG. 5B depicts a memory system 550 in which the same motherboard 505 ofFIG. 5A is populated with two memory modules 115A and 115B. Each memorymodule 115A and 115B is in a half-width mode, meaning that half of theprimary data links of primary data interface 150 are used to communicatedata and the other half are inactive. Only one of the two primary linkgroups for each data-buffer component 135 is used (e.g., primary bufferlink group DQbp[3:0] of slice 125[0]), and motherboard 505 connects onlyhalf of the contacts in each primary data interface 150 to controllercomponent 110. In particular, memory module 115A communicates withcontroller component 110 via primary data ports DQu and thecorresponding half of primary link groups DQp[71:0], and memory module115B communicates with controller component 110 via primary data portsDQv and the other half of the primary link groups. These connections arepoint-to-point, so memory modules 115A and 115B exhibit a lower load onthe data link groups than systems in which two modules share the samedata links. Links DQt[31:0] are not used in this dual-moduleconfiguration.

FIG. 6A depicts memory slice 125[0] with one DRAM component 130B and asubset of the signal lines highlighted to illustrate how multiplexers200, 205, and 210 convey data between primary data link group DQbp[3:0]and one DRAM component in a half-width mode. Address buffer 140, viasecondary command interface QCAB, selects one of the four DRAMcomponents, the rightmost component 130B in this example. Responsive tosignals on buffer control interface BCOM, multiplexers 200, 205, and 210communicate read and write data between the low-order primary link groupDQbp[3:0] and the selected DRAM component; the high-order link groupDQbp[7:4] of the primary data interface is not connected to controllercomponent 110, and is not used in this half-width mode.

FIG. 6B is a waveform diagram 600 illustrating successive readtransactions directed to memory slice 125[0] configured as illustratedin FIG. 6A. Signals associated with the first read transaction areencompassed in bold boundaries to distinguish them from those of thesecond read transaction. The interaction of controller component 110 andslice 125[0] is similar to what is detailed above in connection withFIG. 3B, except that address-buffer component 140 only activates one ofDRAM components 130A and 130B, and slice 125[0] only employs thelow-order link group DQp[3:0] of the primary data interface. Stateddifferently, each slice is configured to deliver half-width data. Eachmodule 115A and 115B (FIG. 5B) thus provides data in four-bit bursts ofnine data nibbles (36 bits), collectively four-bit bursts of 72 bits, tocontroller component 110.

FIG. 7A depicts memory slice 125[0] with DRAM components 130A and thesignal lines highlighted to illustrate how multiplexers 200, 205, and210 convey data between primary link group DQbp[3:0] and a pair of DRAMcomponents in a half-width TDM mode that supports enhanced EDC.Secondary command interface QCAB selects two DRAM components, bothanterior components 130A in this example. Slice 125[0] operates in themanner noted above in connection with FIGS. 4A and 4B, but each memorytransaction communicates with only two DRAM components. Data-buffercomponent 135 interleaves the data from the selected pair, with each ofslices 125[8:0] thus communicating a burst of eight data nibbles foreach read or write transaction initiated by controller component 110.Memory module 115 thus communicates eight sets of nine data nibbles (288bits) in this half-width, enhanced EDC mode.

FIG. 7B is a waveform diagram 700 illustrating successive readtransitions directed to memory slice 125[0] with memory module 115 inthe enhanced EDC mode illustrated in FIG. 7A. Signals associated withthe first read transaction are encompassed in bold boundaries todistinguish them from those of the second read transaction. Theinteraction of controller component 110 and slice 125[0] is similar towhat is detailed above in connection with FIG. 4B, except thataddress-buffer component 140 only activates two of the four DRAMcomponents 130A and 130B, and slice 125[0] only employs the low-ordernibble of primary interface DQp[3:0]. Memory modules 115A and 115Bcollectively activate thirty-six DRAM components, a number sufficientfor the enhanced EDC mode. Each of modules 115A and 115B (FIG. 5B)provides data in eight-bit bursts of 36 bits, allowing controllercomponent 110 to communicate eight-bit bursts of 72 bits on primary datatraces DQp[71:0] for each memory transaction.

FIG. 7C is a waveform diagram 710 illustrating successive readtransitions directed to memory slice 125[0] with memory module 115 inthe half-width enhanced EDC mode illustrated in FIG. 7A. Signalsassociated with the first read transaction are encompassed in boldboundaries to distinguish them from those of the second readtransaction. This example is similar to that of FIG. 7B, but buffer 135communicates over primary links DQp[71:0] at twice the bit rate ofsecondary links DQs[143:0].

FIG. 8 details a portion of memory module 115, introduced in FIG. 1,highlighting features and connectivity that support widthconfigurability and different EDC modes in accordance with oneembodiment. Address-buffer component 140 is shown with one of the ninedata-buffer components 135 and the four DRAM components 130 with whichbuffer 140 directly communicates. DRAM components 130 are distinguishedusing a two-place alphanumeric designation (A0, A1, B0, and B1).

Of the three secondary command interfaces QCAB, QCCD, and QCEF, only theinterface QCAB coupled to the depicted slice is shown in detail; theother two are identical. Command interface QCAB includes multipleconductors with associated signals, to be discussed below. In thisexample, module 115 comprises a printed-circuit board, with components205A0/B0 on one side and components 205A1/205B1 on the other.

Data-buffer component 135 includes two “nibble” data ports DQbp[3:0],DQSp[0]± and DQbp[7:4], DQSp[1]± on the primary side (or “processor”side), where “DQSp[#]±” specifies two-line complementary strobes; andincludes four nibble data ports DQs[3:0], DQSA [0]±; DQs[7:4], DQSA[1]±; DQs[75:72], DQSB [0]±; and DQs[79:76], DQSB [1]± on the DRAM side(or “secondary” side). Commands issued on lines BCOM[3:0] steer and timedata as required in the various operational modes. Signal BCK± is acomplementary clock signal, BCKE is a clock-enable signal that allowsData-buffer component 135 to e.g. selectively power its interfacecircuits for improved efficiently, and BODT controls on-die-terminationelements in Data-buffer component 135 for impedance matching. Thesesignals are generally well documented and understood by those of skillin the art.

Each DRAM component 130 communicates with data-buffer component 135 viaa data-and-strobe port DQ[3:0], DQS±, and communicates withaddress-buffer component 140 over secondary command interface QCAB viaports QAODT[#], QACKE[#], QACS[#]; and QRST,QACA[23:0],QA/BCK±.Components 130 may be conventional, and their input control signals andports are well documented and understood by those of skill in the art.Briefly, signals QAODT[#] control the on-die termination values for eachDRAM component 130; signals QA/BCKE[#] (the “CKE” for “clock-enable”),are used to switch components 130 between active and low-power states;QACS[i] are chip-select signals that determine which of dies 800 isactive for a given memory transaction; QRST is a reset signal common toall components 130; QACA[23:0] are command and address signals; andQACK± is a complementary clock signal that serves as a timing reference.

At the left in address-buffer component 140, the primary links (fromcontroller 110) are CA links DCA[23:0], noted previously; complementaryclock links DCK± that provide timing reference to module 115; andchip-select links DCS[8:0] to specify ranks of memory components 130 foreach memory transaction in the various modes. (In this context, a “rank”is a set of memory dies the controller accesses simultaneously to readand write data.) The “slow signals” that are connected to address-buffercomponent 140 are used for initialization and maintenance operations.

Link group DCA[23:0] includes eighteen address bits A, two bank-addressbits BA, two bank-group address bits BG, an activate bit ACT, and aparity bit PAR. Address-buffer component 140 copies commands andaddresses on links DCA[23:0] to links QACA[23:0] of secondary commandinterface QCAB. Address-buffer component 140 also copies chip-selectinformation on the primary links DCS[3:0] to the requisite traces oflink groups QACS[3:0].

Memory components 130A0 and 130A1 are on the front of module 115,whereas components 130B0 and 130B1 are on the back. Each memorycomponent contains two DRAM dies 800 in this example, which can bestacked as noted in connection with FIG. 2. Other embodiments supportmore or fewer dies per site, depending e.g. on the DRAM packagingoption.

Address-buffer component 140 conveys memory component sub-selectioninformation to data-buffer component 135 via buffer command interfaceBCOM[3:0]. This signal instructs each data-buffer component 135 toaccess components 130A[1:0] or 130B[1:0], each of which includes amemory-component interface DQ[3:0] connected to a respective one of thefour secondary data link groups DQs[3:0], DQs[7:4], DQs[75:72], andDQs[79:76]. Interface BCOM[3:0] can be used for other purposes, such asfor initialization, maintenance, and testing.

Address-buffer component 140 includes a number of circuits that areomitted here. Such circuits may include a phase-locked loop, trainingand built-in self-test (BIST) logic, a command buffer, and a commanddecoder. These and other circuits are well understood by those of skillin the art, and details unrelated to the present disclosure are omittedfor brevity.

Each data-buffer component 135 in the forgoing examples serves fourmemory components 130. Data buffers in accordance with other embodimentscan serve more or fewer. Moreover, while the functions and connectivityprovided by data-buffer components 135 and address-buffer component 140are carried out on separate integrated circuits in the foregoingexamples, some or all of the address-buffer functionality can beintegrated with that of the data buffers.

FIG. 9A depicts a memory system 900 similar to system 500 of FIG. 5A,with like-identified elements being the same or similar. As in thatprior example, motherboard 505 includes two module connectors 510 andprimary data links DQp[71:0] and DQt[35:0]. Half of primary linksDQp[71:0] extend directly to the far connector 510; the other halfextend to the far connector 510 via continuity module 520. System 900thus provides point-to-point data connections between controllercomponent 110 and primary data interface 150 of a single memory module905.

Module 905 is largely as detailed previously. However, the data buffers935 of module 905 have two—rather than four—secondary data interfaces(e.g., secondary interfaces DQs[7:4] and DQs[3:0]). Each of thesecondary interfaces is coupled to a pair of DRAM components 130A and130B. When configured in the full-width mode, as in this example, databuffers 935 communicate data, in the read and write directions, betweenthe primary data interfaces and corresponding secondary data interfaces.Using the example of memory slice 925[0], data buffer 935 relays databetween primary data link groups DQp[7:4] and DQt[3:0] and respectivesecondary data link groups DQs[3:0] and DQs[7:4]. In this mode, addressbuffer 940 alternatively activates either DRAM components 130A or 130Bfor each memory transaction to communicate seventy-two-bit data inbursts of four, or 288 bits. Of nine memory slices 925[8:0], one sliceis used for EDC. As detailed below, data buffers 935 and address buffer940 are modified to support multiple widths and multiple EDC modes.

FIG. 9B depicts a memory system 950 in which the same motherboard 505 ofFIG. 9A is populated with two memory modules 905A and 905B, eachconfigured in a narrow, half-width mode. As in the example of FIG. 5B,only one of the two primary link groups for each data-buffer component935 is used, and motherboard 505 connects only half of the contacts ineach primary data interface 150 to controller component 110. Inparticular, memory module 905A communicates with controller component110 via primary data ports DQu and the corresponding half of primarylink groups DQp[71:0], and memory module 905B communicates withcontroller component 110 via primary data ports DQv and the other halfof the primary link groups.

Memory system 950 supports three EDC modes. The first EDC mode works inthe manner detailed in connection with FIG. 6A, except that theswitching provided by multiplexers 200 and 205 is omitted. Each memorytransaction accesses one DRAM component 130 per memory slice 925[8:0],or eighteen DRAM component 130 between both modules. Each of modules905A and 905B thus communicates thirty-six-bit data in bursts of four,or 144 bits, so that each memory transaction communicates 288 bits. Ofeighteen memory slices 925[8:0], two are used for EDC.

The second EDC mode works in the manner detailed in connection with FIG.7A, again excepting the switching provided by multiplexers 200 and 205.Address buffer 940 activates eighteen DRAM components 130 in each ofmemory modules 905A and 905B, or thirty-six total. DRAM components 130Aare highlighted using bold boundaries to illustrate such an access. Eachdata buffer 935 interleaves four nibbles from each of a selected pair ofmemory components 130 to deliver eight-nibble bursts on one of the twoprimary data link groups. With reference to memory slice 925[0] ofmemory module 905A, for example, data buffer 935 interleaves four-nibblebursts from a pair of DRAM components 130A to deliver eight-nibblebursts on primary link group DQp[7:4]. Memory slice 925[0] of memorymodule 905B likewise delivers eight-nibble bursts on primary link groupDQp[3:0]. As noted previously, primary links DQt[31:0] are not used inthis or the other half-width modes.

FIG. 9C is a waveform diagram 960 illustrating successive readtransitions directed to memory slice 925[0] of memory module 905A ofFIG. 9B in an enhanced EDC mode similar to that detailed previously inconnection with FIG. 7A. Signals associated with the first readtransaction are encompassed in bold boundaries to distinguish them fromthose of the second read transaction.

Address-buffer component 940 activates and reads from two DRAMcomponents 130A, which simultaneously provide four-nibble bursts Q[3:0]and Q[7:4] on secondary interfaces DQs[3:0] and DQs[7:4], respectively.Data buffer 935 interleaves these nibbles to provide an eight-nibbleburst Q[7:0] on primary data link group DQp[7:4]. Memory modules 905Aand 905B collectively activate thirty-six DRAM components 130, a numbersufficient for the enhanced EDC mode that corrects for any single DRAMdevice failure, and any multi-bit errors from any portion of a singleDRAM device.

Bubbles between data bursts on the secondary data links (e.g., DQs[7:4]and DQs[3:0] of FIG. 9C) accommodate the fact that slice 925[0] hastwice as many secondary data links as primary data links. On a secondenhanced EDC mode similar to the one described in connection with FIG.4C, data buffers 935 communicate over primary data links DQp[71:0] attwice the bit rate of secondary data links DQs[71:0]. This embodimentrelaxes the speed requirements for DRAM components 130A and 130B,potentially reducing cost, power consumption, or both.

FIG. 10A depicts a memory system 1000 in which a pair of memory slices125[0], one from each of two memory modules 115A and 115B, areconfigured to support a two-module enhanced EDC mode in which all theDRAM components 130 accessed in a single memory transaction are on thesame module. Address-buffer component 140 (FIG. 1) activates a row inall four DRAM components 130A and 130B to present four-bit data on allfour secondary data ports of data-buffer component 135. Data-buffercomponent 135 interleaves the data from the selected pairs of DRAMcomponents 130 so that slice 125[0] communicates a burst of eightnibbles on each of primary buffer link groups DQbp[3:0] and DQbp[7:4].

The burst of low-order nibbles on buffer link group DQbp[3:0] isconveyed to a primary data port DQu of controller component 110 viaprimary link group DQp[3:0]. The burst of high-order nibbles on bufferlink group DQbp[7:0] is conveyed to a primary data port DQv ofcontroller component 110 via primary link group DQt[3:0], slice 125[0]of the other memory module 115B, and primary link group DQp[7:4]. Noneof memory components 130 in slice 125[0] of memory module 115B isactivated; instead, data buffer 135 relays data on primary buffer linkgroup DQbp[7:4] to primary buffer link group DQbp[3:0].

Relaying data through memory module 115B imposes an additional bufferdelay t_(buf) on the data from primary buffer link group DQbp[7:4]. Databuffer 135 in the active slice 125[0] imposes an additional buffer delayt_(buf) on the burst from primary buffer link group DQbp[3:0], for atotal delay 2t_(buf), to align the nibble-wide bursts to controllercomponent 110. Slice 125[0] of memory module 115A thus communicatesbursts of eight eight-bit words for each read or write transactioninitiated by controller component 110.

FIG. 10B depicts memory system 1000 of FIG. 10A with DRAM components 130of slice 125[0] of module 115B activated in support of a memorytransaction. Data buffer 135 in module 115A relays data on primarybuffer link group DQbp[7:4] from memory module 115B to primary bufferlink group DQbp[3:0]. Slice 125[0] of memory module 115B thuscommunicates bursts of eight eight-bit words for each read or writetransaction initiated by controller component 110.

FIG. 10C is a more complete view of memory system 1000 of FIGS. 10A and10B. Each memory module 115A and 115B is in a full-width mode. Only thelow-order primary buffer link group in each data-buffer component 135(e.g., DQbp[3:0]) is connected directly to controller component 110; thehigh-order primary buffer link group (e.g., DQbp[7:4]) is connected tocontroller component 110 via the other memory module. In this example,controller component 110 initiated a read transaction that activated allthirty-six memory components 130A and 130B in memory module 115A (theactive memory components 130A and 130B are highlighted using boldboundaries). With thirty-six active components, controller component 110can correct for any single DRAM device failure, and any multi-bit errorsfrom any portion of a single DRAM device (e.g., Chipkill™ EDC).

FIG. 10D is a waveform diagram 1050 illustrating a read transitiondirected to memory slice 125[0] of memory module 115A, as illustrated inconnection with FIGS. 10A and 10C. To begin, controller component 110issues an activate command ACT to modules 115A and 115B via CA tracesDCA[26:0]. Responsive to this command, RCD 140 on memory module 115Aactivates a row of memory cells (not shown) in all four DRAM components130A and 130B of slice 125[0]; and RCD 140 on memory module 115Bprepares to forward signals from primary buffer link group DQbp[7:4] toprimary buffer link group DQbp[3:0].

Having activated a row of memory cells in memory module 115A andprepared memory module 115B to forward data, controller component 110issues a read command RD. Address buffer 140 of memory module 115Abuffers these signals and issues them to slice 125[0] via secondarycommand interface QCAB to activate columns of the memory cells withinthe active rows.

Data-buffer component 135 in slice 125[0] of memory module 115A reads aburst of four nibbles from each of the four DRAM components 130A and130B, on respective secondary link groups DQs[7:4], DQs[3:0],DQs[79:76], and DQs[75:72]. Data-buffer component 135 interleaves thedata from secondary link groups DQs[7:4] and DQs[3:0] to provide a burstof eight nibbles on primary buffer data links DQbp[3:0], and thusprimary data links DQp[3:0]. Data-buffer component 135 imposes a secondbuffer delay so that the data on primary buffer link group DQbp[3:0] andprimary link group DQp[3:0] appears two buffer delays 2t_(buf) after theappearance of the data on the secondary link groups. Data-buffercomponent 135 also interleaves the data from secondary link groupsDQs[79:76] and DQs[75:72] to provide a burst of eight nibbles on primarydata links DQq[3:0]. Data-buffer component 135 only imposes one bufferdelay t_(buff); however, the slice 125[0] in the other module 115B (seeFIGS. 10A and 10C) imposes a second buffer delay so that the data onprimary link group DQp[7:4] appears two buffer delays 2t_(buf) after theappearance of the data on the secondary link groups. The eight-nibblebursts on primary link groups DQp[7:4] and DQp[3:0] are thus aligned. Inother embodiments data buffers 135 communicate over primary link groupsDQp and DQt at twice the bit rate relative to the bit rate employed withsecondary links DQs[143:0].

In the foregoing description and in the accompanying drawings, specificterminology and drawing symbols have been set forth to provide athorough understanding of the present invention. In some instances, theterminology and symbols may imply specific details that are not requiredto practice the invention. For example, any of the specific numbers ofbits, signal path widths, signaling or operating frequencies, circuitsor devices and the like may be different from those described above inalternative embodiments.

Also, the interconnection between circuit elements or circuit blocksshown or described as multi-conductor signal links may alternatively besingle-conductor signal links, and single conductor signal links mayalternatively be multi-conductor signal links. Signals and signalingpaths shown or described as being single-ended may also be differential,and vice-versa. Similarly, signals described or depicted as havingactive-high or active-low logic levels may have opposite logic levels inalternative embodiments.

Circuitry within integrated circuit devices may be implemented usingmetal oxide semiconductor (MOS) technology, bipolar technology or anyother technology in which logical and analog circuits may beimplemented. With respect to terminology, a signal is said to be“asserted” when the signal is driven to a low or high logic state (orcharged to a high logic state or discharged to a low logic state) toindicate a particular condition. Conversely, a signal is said to be“de-asserted” to indicate that the signal is driven (or charged ordischarged) to a state other than the asserted state (including a highor low logic state, or the floating state that may occur when the signaldriving circuit is transitioned to a high impedance condition, such asan open drain or open collector condition).

An output of a process for designing an integrated circuit, or a portionof an integrated circuit, comprising one or more of the circuitsdescribed herein may be a non-transitory computer-readable medium suchas, for example, a magnetic tape or an optical or magnetic disk. Thenon-transitory computer-readable medium may be encoded with datastructures or other information describing circuitry that may bephysically instantiated as an integrated circuit or portion of anintegrated circuit. Although various formats may be used for suchencoding, these data structures are commonly written in CaltechIntermediate Format (CIF), Calma GDS II Stream Format (GDSII), orElectronic Design Interchange Format (EDIF). Those of skill in the artof integrated circuit design can develop such data structures fromschematic diagrams of the type detailed above and the correspondingdescriptions and encode the data structures on computer readable medium.Those of skill in the art of integrated circuit fabrication can use suchencoded data to fabricate integrated circuits comprising one or more ofthe circuits described herein.

A signal driving circuit is said to “output” a signal to a signalreceiving circuit when the signal driving circuit asserts (orde-asserts, if explicitly stated or indicated by context) the signal ona signal line coupled between the signal driving and signal receivingcircuits. A signal line is said to be “activated” when a signal isasserted on the signal line, and “deactivated” when the signal isde-asserted.

Mode selection may include, for example and without limitation, loadinga control value into a register or other storage circuit in response toa host instruction, establishing a device configuration or controllingan operational aspect of the device through a one-time programmingoperation (e.g., blowing fuses within a configuration circuit duringdevice production), and/or connecting one or more selected pins or othercontact structures of the device to reference voltage lines (alsoreferred to as strapping) to establish a particular device configurationor operation aspect of the device. The term “exemplary” is used toexpress an example, not a preference or requirement.

While the invention has been described with reference to specificembodiments thereof, it will be evident that various modifications andchanges may be made thereto without departing from the broader spiritand scope of the invention. For example, features or aspects of any ofthe embodiments may be applied, at least where practicable, incombination with any other of the embodiments or in place of counterpartfeatures or aspects thereof. Moreover, some components are showndirectly connected to one another while others are shown connected viaintermediate components. In each instance the method of interconnection,or “coupling,” establishes some desired electrical communication betweentwo or more circuit nodes, or terminals. Such coupling may often beaccomplished using a number of circuit configurations, as will beunderstood by those of skill in the art. Therefore, the spirit and scopeof the appended claims should not be limited to the foregoingdescription. Only those claims specifically reciting “means for” or“step for” should be construed in the manner required under the sixthparagraph of 35 U.S.C. §112.

What is claimed is:
 1. A memory module comprising: a primary datainterface to communicate data responsive to module commands; memorycomponents, including a first memory component and a second memorycomponent; and a buffer component connected between the primary datainterface and each of the first memory component and the second memorycomponent, the buffer component supporting a first access mode and atime-division-multiplexing mode; wherein the buffer component: in thefirst access mode, transports first data between the primary datainterface and one of the first memory component and the second memorycomponent responsive to a first module command; and in thetime-division-multiplexing mode, transports second data between theprimary data interface and each of the first memory component and thesecond memory component responsive to a second module command.
 2. Thememory module of claim 1, wherein the first data is of a first datawidth of a first number of data bits, the second data is of a seconddata width of a second number, greater than the first number, of databits.
 3. The memory module of claim 2, wherein the first number of databits is half the second number of data bits.
 4. The memory module ofclaim 1, wherein the buffer component interleaves first read data fromthe first memory component with second read data from the second memorycomponent in the time-division-multiplexing mode.
 5. The module of claim1, wherein the buffer component conveys the first data to the primarydata interface at a first bit rate in the first access mode, and conveysthe second data to the primary data interface at a second bit rate,wherein the second bit rate is twice the first bit rate in thetime-division-multiplexing mode.
 6. The memory module of claim 1,further comprising a mode register to store a value indicative of one ofthe first access mode and the time-division-multiplexing mode.
 7. Thememory module of claim 1, further comprising a third memory componentand a fourth memory component, the buffer component connected betweenthe primary data interface and each of the third memory component andthe fourth memory component.
 8. The memory module of claim 7, whereinthe buffer component: in the first access mode, transports third data inparallel with the first data between the primary data interface and oneof the third memory component and the fourth memory component responsiveto the first module command; and in the time-division-multiplexing mode,transports fourth data in parallel with the second data between theprimary data interface and each of the third memory component and thefourth memory component responsive to the second module command.
 9. Thememory module of claim 8, the buffer component supporting a narrowtime-division-multiplexing mode, wherein the buffer componentinterleaves the first data with the third data.
 10. A memory modulecomprising: a module command interface to receive module commands; anaddress buffer component coupled to the module command interface toreceive the module commands, the address buffer component including asecondary command interface; memory slices coupled to the primary datainterface and the secondary command interface, each memory sliceincluding: first, second, third, and fourth memory components eachcoupled to the secondary command interface; a data-buffer componentincluding; first, second, third, and fourth memory-component interfacesof a memory-component width and respectively coupled to the first,second, third, and fourth memory components; first and second primarydata interfaces, each of the memory-component width, to communicatemodule data responsive to the module commands; and multiplexing logic toconvey; in a first access mode, first data from only two of the first,second, third, and fourth memory components responsive to a first modulecommand; and in a time-division-multiplexing mode, second data fromsuccessive pairs of the first, second, third, and fourth memorycomponents responsive to a second module command.
 11. The memory moduleof claim 10, wherein the address buffer component is coupled to thedata-buffer components to control the multiplexing logic.
 12. The memorymodule of claim 11, wherein the address buffer component furthercomprises a mode register to store a value indicative of one of thefirst access mode and the time-division-multiplexing mode.
 13. Thememory module of claim 10, wherein the first data is of a first datawidth of a first number of data bits, and the second data is of thefirst data width.
 14. The memory module of claim 13, wherein thedata-buffer component of each of the memory slices supports a secondtime-division-multiplexing mode, wherein the multiplexing logicinterleaves third data of a second data width half the first data widthfrom only two of the first, second, third, and fourth memory components.15. A memory module comprising: a primary data interface having primarydata links; memory components; and at least one data buffer componentconnected between the primary data interface and the memory components,the at least one data buffer component supporting a full-width mode, ahalf-width first access mode, and a half-widthtime-division-multiplexing mode; wherein the at least one data buffercomponent: in the full-width mode, communicates first data between thememory components and all the primary data links responsive to a firstmodule command; in the half-width first access mode, communicates seconddata between a number of the memory components and half of the primarydata links responsive to a second module command; and in the half-widthtime-division-multiplexing mode, communicates third data between twicethe number of the memory components and half of the primary data linksresponsive to a third module command.
 16. The memory module of claim 15,wherein the third module command comprises a read command, and whereinthe at least one data buffer component interleaves the third data fromthe number of memory components responsive to the read command.
 17. Thememory module of claim 15, wherein the at least one data buffercomponent communicates the third data with the twice the number of thememory components at a first bit rate, and communicates the third datawith the primary data interface at a second bit rate twice the first bitrate.
 18. The memory module of claim 15, wherein the primary data linksconsist of eighteen groups of nibble-wide data link groups, and whereinthe at least one data buffer component communicates four sets of ninedata nibbles responsive to the second module command and eight sets ofnine data nibbles responsive to the third module command.
 19. The memorymodule of claim 18, wherein the at least one data buffer componentcommunicates four sets of eighteen data nibbles responsive to the firstmodule command.
 20. The memory module of claim 19, the at least one databuffer component supporting a second full width mode in which that atleast one data buffer component communicates eight sets of eighteen datanibbles responsive to a fourth module command.
 21. A data buffercomponent comprising: an interface to couple to memory components; aprimary data interface to receive module commands; and circuitry tosupport a full-width mode, a half-width first access mode, and ahalf-width time-division-multiplexing mode, wherein: in the full-widthmode, the data buffer component communicates first data between thememory components and all the primary data links responsive to a firstmodule command; in the half-width first access mode, the data buffercomponent communicates second data between a number of the memorycomponents and half of the primary data links responsive to a secondmodule command; and in the half-width time-division-multiplexing mode,the data buffer component communicates third data between twice thenumber of the memory components and half of the primary data linksresponsive to a third module command.